Some possible causes for dark skin on the inner thighs are hormonal imbalance, obesity and sun exposure, according to Dr. Nima Shei, writing for PositiveMed. Other causes may include certain medications, skin friction and a condition called Acanthosis Nigricans.
PositiveMed explains that darkened inner thighs are quite common and can stem from a wide variety of causes. Razors, lotions, or creams and heavy sweating are all possible reasons for the condition. Although it may be a source of embarrassment for some, the condition is typically not painful, and there are some remedies that may prove helpful in lightening the dark skin between the thighs. Lemon may be used to bleach the skin, says PositiveMed. Likewise, sliced potatoes can also be used as a bleaching tool by pressing them onto the affected areas of the skin for 30 minutes, then washing off with warm water and patting the skin dry.
Oatmeal and yogurt can be mixed together into a paste and used as an exfoliant for the skin. This may be effective for helping to smooth out and lighten dark spots on the thighs. Aloe Vera gel can also be used to reduce inflammation and heal damaged skin, suggests Dr. Shei.